A major goal of tissue repair and regeneration is to develop a biological alternative in vitro for producing an implantable structure that serves as a support and speeds regenerative growth in vivo within a defect area.
In recent years biodegradable polymers such as poly(glycolic acid), poly(L-lactic acid)(PLLA) and their copolymers poly(L-lactic-co-glycolic acid) (PLGA) have been used as scaffold materials in studies of tissue formation (Sofia S., Functionalized silk-based biomaterials for bone formation, J. Biomed. Mater. Res., 54(1):139-148 (2001)). Advantages of these polymers include their biocompatibility and degradability. However, PLGA can induce inflammation due to the acid degradation products that result during hydrolysis (Sofia, S., (2001)). There are also processing difficulties with polyesters that can lead to inconsistent hydrolysis rates and tissue response profiles. Thus, there is a need for polymeric materials that have more controllable features such as hydrophobicity, hydrophilicity, structure, and mechanical strength, while also being biocompatible and/or bioresorbable. Biological polymeric materials often demonstrate combinations of properties which are unable to be reproduced by synthetic polymeric materials. (Perez-Rigueiro et al. Science, 1998; 70: 2439-2447; Hutmacher D. Biomaterials 2000. 21, 2529-2543). For example, scaffolds for bone tissue regeneration require high mechanical strength and porosity along with biodegradability and biocompatibility.
Silk fibroin isolated from Bombyx mori silkworm cocoons has been employed as a matrix material in many tissue engineering applications (Altman G H, et al Biomaterials 2003; 24(3):401-16; Wang Y, et al. Biomaterials 2006; 27(36):6064-82; Kim H J, et al. Macromol Biosci 2007; 7(5):643-55; Hofmann S, et al. Biomaterials 2007; 28(6):1152-62; Wang Y, et al Biomaterials 2006; 27(25):4434-42; Meinel L, Bone 2006; 39(4):922-31; Hofmann S, et al. Tissue Eng 2006; 12(10):2729-38; Altman G H, et al. Biomaterials 2002; 23(20):4131-41) due to its mechanical properties (Heslot H. Biochimie 1998; 80(1):19-31), biocompatibility (Meinel L, et al. Biomaterials 2005; 26(2):147-55), slow degradation profile (Horan R L, et al. In vitro degradation of silk fibroin. Biomaterials 2005; 26(17):3385-93), and aqueous processibility (Wang X, et al. J Control Release 2007; 117(3):360-70; Wang X, et al. J Control Release 2007; 121(3):190-9; Li C, et al. Biomaterials 2006; 27(16):3115-24; Karageorgiou V, et al. J Biomed Mater Res A 2006; 78(2):324-34; Wang X, et al. Langmuir 2005; 21(24):11335-41; Kim U J, et al. Biomaterials 2005; 26(15):2775-85; Nazarov R, et al. Biomacromolecules 2004; 5(3):718-26; Kim U J, et al. Biomacromolecules 2004; 5(3):786-92; Jin H J, et al. Biomaterials 2004; 25(6):1039-47; Jin H J, et al. Biomacromolecules 2002; 3(6):1233-9). The mechanical properties of the silk fibroin protein can be attributed to the formation of an extended crystalline β-sheet structure that is composed of recurrent sequences of glycine, alanine and serine amino acids (Heslot, H., (1998); Lotz B, et al. Biochimie 1979; 61(2):205-14; Zhou C Z, et al. Proteins 2001; 44(2):119-22). The extent of β-sheet structure formation can be controlled through physical (Kim U J, et al. (2005); Valluzzi R, et al. Philos Trans R Soc Lond B Biol Sci 2002; 357(1418):165-7) or chemical methods (Winkler S, et al. Biochemistry 2000; 39(41):12739-46; Matsumoto A, et al. J Phys Chem B 2006; 110(43):21630-8; H.-J. Jin J P et al, 2005; 15(8):1241-1247), leading to materials with controlled crystallinity and degradation rate. In order to further enhance robust tissue formation in vitro using silk as a scaffolding material, tailoring the interaction between these scaffolds and human bone marrow-derived mesenchymal stem cells (hMSCs) is desirable. Adult hMSCs offer potential for regenerative therapies, as they are able to differentiate into bone (Kraus K H, Kirker-Head C. Vet Surg 2006; 35(3):232-42; Mauney J R, et al. Tissue Eng 2005; 11(5-6):787-802), cartilage (Djouad F, et al. Regen Med 2006; 1(4):529-37; Magne D, et al. Trends Mol Med 2005; 11(11):519-26), fat (Neumann K, et al. J Cell Biochem 2007; Mauney J R, et al. Biomaterials 2005; 26(31):6167-75), muscle (Pittenger M, et al. J Musculoskelet Neuronal Interact 2002; 2(4):309-20), and ligament (Vunjak-Novakovic G, et al. Annu Rev Biomed Eng 2004; 6:131-56) cell lines.